I think you may be confusing the ballscrew locking up with the motor stalling because you are asking too much of it. Now is the ballscrew actually jamming or something or does it just quit turning? Once you exceed a certain speed/torque threshold, the stepper will stop spinning and will just vibrate wildly until the motion is finished and it is allowed to accelarate at an acceptable rate again.
You can try reducing the acceleration rate so that it has a smoother speed up which would reduce stalling. Also make sure your bearing s and everything are free so you have no binding. If everything looks good mechanically then you just have to make do with the speeds which are reliable or buy a bigger motor to prevent exceeding its torque output at speed.